The present invention relates to object identification systems and in particular to an improved self-cleaning label for use in such systems.
In U.S. Pat. No. 3,225,177 which is commonly assigned with the present application, a system for the automatic identification of objects is disclosed. The commercial form of the invention is marketed under the trade name KARTRAK by the Servo Corporation of America of Hicksville, New York. The KARTRAK system is the American Association of Railroads' approved form of railroad car identification and, accordingly, virtually every freight car and locomotive in service in the United States and Canada is furnished with a KARTRAK label.
The label comprises a plurality of stripes formed of retroreflective material arranged in a two-position, base 4 code. At various sites, such as freight yards, terminals, etc. scanners are provided which, in effect, "read" the labels to decipher the alpha-numeric data identifying the cars. In this manner, automated surveillance can be maintained of the millions of railroad cars across the country.
The KARTRAK labels comprise a vertical array of modules of parallel, horizontal stripes, each module having two horizontal stripes. The fields are colored blue, orange, black (the absence of blue or orange) or white (the presence of both blue and orange). The modules are coded to contain information as to the car identification number, carry identification code and equipment code as well as control modules which generate a start signal, a stop signal and parity check code. The standard KARTRAK label contains 13 color-coded modules.
In addition to their use on railroad cars, the KARTRAK labels are also used on containers, truck trailers and the like. Indeed, such color-coded labels can be used in many other types of object identification systems. One of the principal advantages of the KARTRAK system is that the object may be moving while its label is being scanned and decoded.
One of the principal problems encountered with such labels is that with time and constant exposure to railroad track conditions the labels become dirty resulting in degradation of the reflected output signal. While the problem could obviously be solved if the label was subject to a regular cleaning program, this is not readily feasible. Heretofore, attempts have been made to electronically compensate for dirty labels during the label reading operation (see, for example, U.S. Pat. No. 3,502,888). This method also has its shortcomings in that sophisticated and hence expensive electronics and optics must be employed. In addition, if the label degrades beyond a certain point, it cannot be compensated for electronically.
In view of the above, it is the principal object of the present invention to provide an improved label particularly for use in identification systems of the type described in the aforereferenced U.S. Pat. No. 3,225,177.
A further object is to provide such a label which, through its construction, is self-cleaning so as to minimize the tendency of dirt to collect on the label stripes and hence prolong the useful life of the label.